In ADHD, Brain Maturation Follows Normal Pattern but Is Delayed

Marlene Busko

May 07, 2008

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Interview with Dr. Shaw

May 7, 2008 (Washington, DC) — A large neuroimaging study found that in attention deficit/hyperactivity disorder (ADHD), brain development follows a normal trajectory, but maturation of the prefrontal cortex — which is important for the control of action and attention — is delayed by about 3 years.

"The hope is that 1 day we can develop neuroimaging so that it can inform decisions about individual children with ADHD, so that we can tailor their treatment," lead study author Philip Shaw, MD, from the National Institute of Mental Health (NIMH), in Bethesda, Maryland, said in a press conference about this study at the American Psychiatric Association 61st Annual Meeting.

The study was recently published (Proc Natl Acad Sci 2007;104:19649-19654.).

"If you show that ADHD is due to a delay in brain development, perhaps we should be looking at factors that disturb the timing of how the brain develops," Dr. Shaw told Medscape Psychiatry. For example, his team is looking at processes of switching on and off genes that sculpt the cortex of the brain, he added, to look for further clues about what is going wrong in ADHD.

Abnormal Development or Delayed Development?

In any average classroom in the United States, 2 children have ADHD, Dr. Shaw said in the press conference. "The first step toward getting better treatment for these children is to try to get a better understanding of the fundamental nature of what's happening in their brains," he said.

Since ADHD was first described, there has been a debate about whether it is due to a delay in brain development or to a complete deviation away from patterns of typical brain development, he added.

Their team sought to answer this question by using computational neuroanatomic techniques to estimate the cortical thickness at more than 40,000 cerebral points from more than 800 magnetic resonance scans from 223 children with ADHD and 223 typically developing controls.

Participants were scanned in adolescence, when childhood cortical thickening gives way to thinning as unused neural connections are pruned for optimal efficiency, an NIMH press release explains.

"With this sample size, we could define the growth trajectory of each cortical point, delineating a phase of childhood increase followed by adolescent decrease in cortical thickness. . . . From these trajectories, the age of attaining peak cortical thickness was derived and used as an index of cortical maturation," the group writes in the study abstract.

They found that among 223 youth with ADHD, half of the 40,000 cortex sites attained peak thickness at an average age of 10.5 years, compared with age 7.5 years in a matched group of youth without the disorder.

In healthy children, there is a wave of brain development starting at the back of the brain, and the last part of the brain that matures is the frontal brain area, which is particularly important for the control of action and attention, Dr. Shaw said.

"The sequence in which the different parts of the brain mature is very similar in the 2 groups," he reported, adding that if ADHD were due to a complete derailing of the normal trajectory of brain development, then this sequence would not be preserved. "I think this is probably quite good evidence that a large component of ADHD is due to delay in brain development," he said.

Brain imaging is still not ready for use as a diagnostic tool in ADHD, he cautioned, noting that although the delay in cortex development was marked, it could be detected only when a very large number of children with the disorder were included, and it is not yet possible to detect such delay from the brain scans of a single individual.

This delayed pattern of maturation observed in ADHD differs from the brain development pattern in autism, which is characterized by brain overgrowth, he added.

Dr. Shaw did not provide any financial disclosure.

American Psychiatric Association 161st Annual Meeting: Symposium 34. May 3-8, 2008.


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